The collection, retention and flow of fluids in tissues are related to their state of health and disease. The long term goal of this work is to image the effective compressibility properties and simultaneously track fluid movement over a wide range of time constants in tissues in vivo, in real time and at high signal-to-noise ratios and diagnostic ultrasound resolutions, and relate them to disease. To accomplish this goal we propose the use of new elastographic methodologies for the direct, noninvasive assessment of local changes in stiffness and compressibility of tissues. This technology may become a new imaging tool that is based on new intrinsic contrast mechanisms for the detection and staging of various diseases. In particular, we envisage at least three important medical areas related to cancer where the development of such a technology may make a significant contribution. These are the areas of lymphedema (primarily in cancer patients), the detection of cancers and their differentiation from normal tissues via the visualization of fluid transport characteristics, and the monitoring of cancer therapies based on altered mechanical and fluid transport parameters. The hypothesis of the present exploratory study is that it is possible to characterize the performance bounds of these novel elastographic techniques to predict their realistic performance levels in applications of clinical interest. The following aims are included in this investigation: 1. Develop and extend simulation tools to model and image the time-dependent mechanical behavior of homogeneous and non-homogeneous poroelastic materials in a variety of complex experimental conditions; 2. Investigate the theoretical upper bounds and tradeoffs in the objective image quality parameters of effective Poisson's ratio elastograms, poroelastograms and effective Poisson's ratio time constant elastograms; 3. Investigate the effect of clinically realistic de-rating (corrupting) factors such as fundamental mechanical limitations, ultrasonic frequency-dependent attenuation, frame rate and realistic decorrelation noise on the attainable objective image quality in vivo. [unreadable] [unreadable] [unreadable]